This invention relates generally to the electrical design and mechanical packaging of electronic components, and more particularly to a method of power conversion utilizing a multiple transformers primaries in series and secondary in parallel.
One approach to packaging electric components in power converters (FIG. 1) includes a housing which both encloses the components and means of heat extraction from the components. The house includes a non-conductive casing 5 and an aluminum heat-sinking base. A printed circuit board (PCB) 3 is mounted next to the upper wall 5a of the casing. Conductive pins 7 are attached directly to the PCB 3 and extend up through the wall 5a. Electronic components 9a, 9c are mounted to one or both sides of the PCB 3. Larger side components such a the transformer 9c are mounted to the lower side for space reason. Power dissipating devices such as 9b are mounted directly on the base-plate 6 for better heat transfer. The power components 9b are electrically connected to the PCB by leads 12. Some of the power dissipating devices, 9d, are attached to the base plate via a thermally conductive insulator material 8. Structure 1 may be fitted with an encapsulant, which acts as a heat spreader and provides mechanical support. In the case when a hard epoxy encapsulant is used a xe2x80x9cbuffer coatingxe2x80x9d material is used to protect some of the components.
In the multiple transformer configuration of this invention, the use of multiple transformers is not new. These multiple secondaries (parallel or not) provide for equal currents but these currents get constricted in the rectifiers and output chokes. Using this type of structure requires large, expensive output chokes and special high current rectifiers which take up precious PCB space. Another drawback to the standard topology is that as device characteristics change over time in the rectifiers and transformers, the currents in the secondaries become more unbalanced while adversely affecting the flux densities in the transformers.
It is clear that there is a need for an improved circuit for multiple transformer systems.
This invention is related to the electrical design and mechanical packaging of electronic components. It involves a new method of power conversion utilizing a multiple transformers primaries in series and secondary in parallel (or vice versa).
Within the present invention, a transformer group is created in which a multitude of transformers are used to supply energy to a single load. The transformers are connected in series; in order to assist in providing a xe2x80x9cflux equalizingxe2x80x9d affect, the invention includes a flux equalizer circuit. The flux equalizer circuit provides a series of flux windings. Each flux winding is associated with a single transformer. The windings are arranged in a closed loop. In this manner, a balancing of the output of the transformers is obtained; the flux swing from each transformer is xe2x80x9csensedxe2x80x9d by its associated flux winding which is xe2x80x9csharedxe2x80x9d with the other transformers via their own associated load winding.
As background, the invention provides a packaging technology for power converters and power magnetics. The packaging methodology provides a compact, inexpensive, easy to manufacture. The invention features a package for electrical components held on a circuit board. In this packaging concept most of the power magnetic elements are constructed into the multilayers PCB. The windings of the magnetic elements such as transformer, inductors, and in some cases event signal transformers are incorporated in the multilayers PCB. The top layer and some portion of the bottom layer are also support for electronic components. The windings of the magnetic elements are contained inside of the multilayers PCB; the electronic components are placed on the top and on the bottom of the PCB. Some of the components are located on top of the windings and the interconnections between the magnetic elements. In this way the footprint of the magnetic elements is reduced to the footprint of the transformer core. The power-dissipating devices replaced on pads, which have a multitude of copper coated via to the other side of the PCB. The heat transferred to the other side of the PCB can be further spread using a larger pad or transferred to a metallic base-plate attached to the PCB through an isolating material. For air-cooled due to the limited surface of the heat spreader, an additional heat sink is attache to the heat spreader to increase its cooling area.
The unique aspect of this packaging concept is the fact that the magnetic element""s windings are incorporated on the multilayers PCB construction which also serves as a support for power-dissipating components and some of the control components. The heat from the power-dissipating components is extracted through copper coated via which transfer the heat to the other side of the PCB. The heat is further transferred to a metal base plate connected to the PCB via a thermally conductive insulator. For airflow cooling applications the heat spreader connected to the thermal via can serve as a cooling surface. A heatsink can be also attached to the heat spreader to increased the heat dissipation area.
In the multiple transformer configuration of this invention, in order to ensure that the flux level is kept proper for each of the transformers, another secondary winding is added to each transformer to force that the flux densities in each transformer to be equal. In addition, the outputs are paralleled after the output chokes so the currents are spread over multiple secondaries each complete with their own rectifiers and output chokes.
The invention, together with various embodiments thereof, will be more fully explained by the accompanying drawings and the following descriptions.